Method of reducing the length of oversize fibers



Oct. 8, 1968 V LANE 3,404,592

METHOD OF REDUCING THE LENGTH OF OVERSIZE FIBERS Filed Nov. 21, 1966 United States Patent 3,404,592 METHOD OF REDUCING THE LENGTH i s -0F OVERSIZE FIBERS Frederick H. Lane, Water 0'rt0n,Birmingham, England, assignor to'The Dunlop Company Limited, London, England, a British company i 7 Filed Nov. 21, 1966, Ser. No. 595,704 Claims priority, application Great Britain, Nov. 27, 1965,

6 Claims. (CI. 83-16) This invention relates to a method of treating textile flock to reduce the length of oversize fibres, and to apparatus suitable for use in said method. The invention relates particularly to a method and apparatus for treating textile flock to improve its suitability for use in the production of carpets by a process of electrostatic flock deposition. Such carpets are obtained by the electrostatic deposition of textile flock onto a base material, for instance a rubber sheet coated with adhesive. In general, a suitable length of fiock fibres is about 3 mm., though it is not essential that all the fibres should be of uniform length, and under normal conditions such flock would contain fibres varying in length from about 2 /2 to 5 mm. However, in one method of producing flock suitable for elecstatic deposition, there occur a proportion of excessively long fibresin making 3 mm. flock for instance some fibres may be up to about 25 mm. in length-and these interfere seriously with the electrostatic deposition. During deposition the presence of these oversize fibres when attached to the rubber backing has the effect, since they stand up well above the general level of the other fibres, of distorting the lines of force and thereby shielding the surrounding areas. The result is that only a few fibres are deposited in the area immediately surrounding each oversize fibre, and a creater is formed in the pile which spoils its appearance. Consequently it is necessary to separate the oversize fibres from the flock before using it in the electrostatic process. The method hitherto adopted to achieve the necessary separationhas been to sieve the flock using as a sieve a vibrating perforated plate so that the oversize fibres pass over the plate and the small ones fall through its perforations. However, this method of separation suffers from the disadvantage that some of the oversize fibres pass through the holes of the sieve endways and it is therefore necessary to pass the sieved material through the sieve several times in order to ensure the removal of all oversize fibres. This is inconvenient and uneconornical as the output of the machine is considerably limited by the necessary repetition of the process.

According to the present invention we have now devised a method which in effect removes the oversize fibres from a textile flock in a very simple yet convenient and etficient way. Accordingly, the invention provides in one aspect a method of treating a textile flock to reduce the length of oversize fibres, which comprises causing the fibres of the fiock to adhere by their ends to a surface so that they project substantially at right angles from said surface and are substantially parallel to each other, trimming the pile thus obtained on said surface to reduce the length of the oversize fibres and then separating the trimmed pile from said surface.

A very convenient way of causing the fibres to adhere to the surface is by means of electrostatic attraction which in effect provides a temporary pile carpet having the said surface as its backing. The surface is preferably in the form of an endless belt coated with a liquid medium which acts as a temporary adhesive to hold the fibres in position. A satisfactory form of belt is a canvass belt 3,404,592 Patented Oct. 8, 1968 wetted with water, for example by passing it through a bath of plain water before subjecting it to the electricallycharged textile flock.

As the means of reducing the length of the oversize fibres we have found it very convenient to use a heated wire, or like cutter especially where the fibers to be out are of a thermoplastic polymer, for instance a poly-amide or polyacrylonitrile. The heated cutter, when it impinges on the oversize fibres, causes local burning or melting of the fibres resulting in the severing of the excess length of fibre. The cutter is preferably mounted so that its distance from the pile can be adjusted so as to reduce the oversize fibres to any desired length. The exact distance, of course, depends on the length of fibre desired from the method. It should be noted that where the textile flock is of a thermoplastic polymer the melting which accompanies the cutting operation usually results in a slight discoloration of the polymer, and though this is insignificant where the proportion of the number of fibres being cut is small, if the proportion is large the operation may result in undesirable coloration of the flock obtained. The method of the invention is therefore best applied to a fiock having only a small proportion of oversize fibres. Where the surface carrying the temporary pile is an endless belt it is convenient to have the heated cutter arranged with respect to the belt surface so that the ends of the oversize fibres removed by the cutter can fall under gravity into a suitable container. Preferably the fibres pass the cutter at the point where the belt is vertical.

Where the fibres are held to the said surface by means of a temporary adhesive such as water, it has been found convenient to remove them by means of a scraper which is preferably arranged so that the fibres scraped from the surface can fall under gravity into a container. Where the temporary adhesive is water the flock removed from the surface is normally damp and requires drying before being used in any subsequent process of electrostatic deposition in the making of carpets.

The means of dispensing the flock and of charging it electrostatically to produce a pile surface can be any means conventionally known for the deposition of textile flock by electrostatic means. For example the dispenser is conveniently a hopper whose bottom is in the form of a metal grid having any suitable potential, for instance 30-100 kv., and having means to feed textile flock through the grid at a predetermined rate. Where the dispenser is connected, as is conventionally the case, to the positive side of a generator, the said surface is preferably connected to the negative (earth) side of the generator.

There follows a description, with reference to the accompanying drawing, of a preferred embodiment of the apparatus of the invention.

In the drawing A is a dispenser for flock to be treated by the method of the invention and comprises a container A whose base is a wire grid A of about A inch mesh, and a revolving brush with nylon bristles A mounted inside the dispenser to brush flock at a uniform rate through the grid. The grid is maintained at a suitable negative potential relative to earth by means of an Extra High Tension generator E capable of supplying a potential of up to kv. The positive side of the generator is earthed. The hopper is 18 inches long by 18 inches wide and the brush has an overall diameter of 12 inches. Although the holes of the grid are only approximately 6 mm. square, fibres up to 25 mm. in length can be brushed through them.

An endless canvas belt B 18 inches wide (preferably having a rubber coating on its outer surface so that the overall thickness of the belt is 1 mm.) is carried by a driving roller C having a diameter of 3% inches, (which is connected to the negative side of the generator) and a roller F having a diameter of 1 inch. The clearance be tween the grid A and the belt B is 4 inches. D is a tank containing plain water in which the lowermost part of the belt is immersed.

A heater wire G, 22 inches long, made of an alloy, Brightrray C, normally used for electric heaters, is fitted parallel to the axis of roller F and 5 mm. away from it. This wire burns through all the fibres projecting more than the required height, and this height can be adjusted to suit requirements, by moving the supports which carry a fixed insulated terminal and an insulated pulley. One end of the wire is attached to the fixed insulated terminal, and the other end is attached to a cord passing over the insulated pulley and has a weight attached to the free end. A flying lead is attached to this end of the heater wire to carry the current to it. The heater Wire is 0.014 inch in diameter and is maintained at a dull red heat by passing through it a current of 5 amps from a Variac, and the cord and weight system keep the wire taut under all conditions. J and J are scraper blades, having lightly rounded edges, made of Tufnol (a thin phenol formaldehyde/cloth laminate), and H and K are containers for flock removed by the wire G and scrapers J and J respectively. Behind the scrapers is a fixed brush L with nylon bristles, which presses against the surface of the belt to remove any fibres left behind. It is found desirable to prevent fibres from being carried back into the water tank or being left behind on the belt, since they prevent the untreated flock from depositing as the uniform layer needed for satisfactory cropping. It is also found desirable periodically to interrupt the current maintaining the electric field, since the flock falling from the hopper has a tendency to form strings hanging from the grid, which foul the pile formed on the belt, and periodic interruption of the field disperse these strings. The strings can also be dispersed by mechanically breaking them up, without interrupting the field.

There now follows a description of a specific embodiment of the method of the invention using the apparatus described above with reference to the drawings.

A flock of denier polyacrylonitrile fibres sold under the trademark Courtelle comprising a major proportion of fibres of about 3 mm. length but also containing 0.5% by weight of fibres of oversize length up to mm. long is fed to the dispenser A at a rate of 23 lbs. (dry weight) per hour. A potential of 50 kv. is applied to grid A and an electric current (approximately 5 amperes) is passed through wire G so as to bring it to red heat. The belt B is set in motion in a clockwise direction about rollers C and F, at a speed of 6 /2 feet a minute, and the revolving brush meter A is set in motion thereby feeding electrostaticallycharged flock fibres through the grid A on to the belt B (which has by this time been wetted by passage through water bath D). The charged fibres falling on to the belt B adhere, as a pile, substantially at right angles to the belt and substantially parallel to each other, the water acting as: an adhesive Thetposition of wireG with relation to the belt B is adjusted so that;it impinges only on the fibres of oversize length, and, being red hot, melts them ,at the points of contact thereby cutting offtheir ends. The ends of the fibres thus trimmed. fall into the containerH, and the trimmed pile of fibres is removed from the belt by the' scrapers and fall 'into the container K thereby'pro viding a flock which is free from fibres over 4 mm. long. The flock thus removed from the belt contains about 6% of water and is then dried. The fiock is then deposited by electrostatic means on a rubber backing coated with adhesive. The resulting carpet has a uniform depth of pile with no craters.

The fibre ends collected in container H can be dried and returned to dispenser A for re-use.

Having now described my invention, what I claim is:

1. A method of treating a textile flock to reduce the length of oversize fibres, which comprises causing the fibres of the flock to adhere by their ends to a surface so that they project substantially at right angles from said surface and are substantially parallel to each other, trimming the pile thus obtained on said surface to reduce the length of the oversize fibres and then separating the trimmed pile from said surface.

2. A method according to claim 1, in which the fibres adhere to the surface by means of electrostatic attraction.

3. A method according to claim 2, in which the surface is in the form of an endles belt coated with a liquid medium.

4. A method according to claim medium is water.

5. A method according to claim 1, in which the flock is is of a thermoplastic polymer and-is trimmed by a heated cutter.

6. A method according to claim 3, wherein the fibres pass the cutter at the point where the belt is vertical.

3, in which the liquid References Cited UNITED STATES PATENTS 2,998,051 8/1961 Sittel 19--144 3,142,279 7/1964 Rubin 83-16 X 3,199,388 8/1965 Redfiel d 83-171 X ANDREW R. JUHASZ, Primary Examiner. 

1. A METHOD OF TREATING A TEXTILE FLOCK TO REDUCE THE LENGTH OF OVERSIZE FIBRES, WHICH COMPRISES CAUSING THE FIBRES OF THE FLOCK TO ADHERE BY THEIR ENDS TO A SURFACE SO THAT THEY PROJECT SUBSTANTIALLY AT RIGHT ANGLES FROM SAID SURFACE AND ARE SUBSTANTIALLY PARALLEL TO EACH OTHER, TRIMMING THE PILE THUS OBTAINED ON SAID SURFACE TO REDUCE THE LENGTH OF THE OVERSIZE FIBRES AND THEN SEPARATING THE TRIMMED PILE FROM SAID SURFACE. 